The present invention relates to an improved in-line electron gun structure which has a quadrupole electrode forming an improved quadrupole lens, and more particularly relates to a color cathode ray tube having an improved in-line electron gun structure which can minimize a change in the convergence and spherical aberrations when a modulated voltage is applied, thereby improving resolution characteristics in the peripheral areas of a screen and convergence characteristics.
In general, a deflection yoke system employs a self-convergence deflection yoke in which magnetic fields are non-uniformly transformed into a pin-cushion-type magnetic field in the horizontal deflection and a barrel-type magnetic field in the vertical deflection for removing a dynamic convergence circuit. Thus a spot shape of an electron beam is distorted in the peripheral areas of the screen due to a strong magnetic field of the deflection yoke. This spot shape remarkably changes the resolution at the peripheral areas, so that, in a dynamic focus type, the modulated voltage increased at the peripheral areas is superposed to the focus voltage Vf applied to the convergence electrode, thereby making the spot shape circular in the peripheral areas. In this dynamic focus type, the resolution in the peripheral areas becomes improved, but the convergence action of the main lens to be formed between an anode electrode and a convergence electrode is changed according to the modulation of the focus voltage Vf, thereby causing the problem of the convergence deterioration wherein the spots of opposite side electron beams R and B deviate from the spot of an electron beam G. Meanwhile, to obtain a circular spot shape in the peripheral areas of the screen, several electron gun system are proposed, in which electrodes forming a quadrupole lens are disposed for correcting the transformation of the electron beam in the peripheral areas by using a static electricity.
FIG. 1 is a sectional view of a conventional in-line type electron gun. As shown in FIG. 1, three cathodes 5 are disposed on one horizontal straight line for radiating three electron beams. Above the three cathodes 5, there are provided with a common control electrode 10, a first screen electrode 20, a accelerating electrode 30, a second screen electrode 40, a first focusing static electrode 50 to which a static voltage is applied, a second focusing dynamic electrode 55 to which a dynamic voltage is applied, an anode electrode 60 constituting a main lens and a convergence cup 70. These components are arranged in this order in the dynamic focus type electron gun system, in which electrodes 50 and 55 comprise a quadrupole lens for correcting the spot shape of the electron beam in the peripheral areas of the screen.
FIG. 2 is an exploded perspective view of the electrodes 50 and 55. Used as a quadrupole lens, three electron-beam-passing apertures 50a, 50b and 50b are punched in the electrode 50, on which plate-like protrusions 50c and 55d are attached. The electrode 55 includes inwardly-bent barriers 55a, between which the plate-like protrusions 50c and 50d are inserted, thereby making a quadrupole lens.
However, in such arrangement it is very difficult to integrate the electrodes and to assemble them due to its construction. And, since a pair of the barriers 55a arranged horizontally is common for the three electron beams, the convergence characteristics is deteriorated due to the electric field formed between the central electron-beam-passing aperture 50a and the barriers 55a. That is, when one quadrupole lens is adapted and the dynamic voltage Vf2 is applied, the intensity of the lens on the vertical axis becomes strong. Thus, the edge of the electron beam on the horizontal axis tends to become enlarged and the core of the electron beam on the horizontal axis tends to become small.
Therefore, the present invention has been made to overcome the above described problems of the prior arts, and accordingly it is an object of the present invention to provide a color cathode ray tube having an improved electron gun, further comprising a quadrupole lens which consists of an independent static electrode to which a static voltage is applied and a dynamic electrode which is disposed opposite to the independent electrode and a dynamic voltage is applied to the dynamic electrode. A strong dynamic quadrupole lens effect is obtained by applying a modulation voltage or parabola voltage to the dynamic electrode.
Also, while enlarging electron-beam-passing apertures in electrodes of a main lens, each axial distance between the axes of three electron-beam-passing apertures of the static electrode opposite to a dynamic electrode in the strong-quadrupole-lens-forming electrodes is offset and the size of the opposite side electron-beam-passing apertures is increased by the offset axial distance. Thus, a change in the convergence and spherical aberrations when a modulated voltage is applied can be minimized, thereby improving resolution characteristics in the peripheral areas of a screen and convergence characteristics.
The present invention has been made to overcome the above-described problems of the prior art.
Accordingly, it is an object of the present invention to provide a color cathode ray tube having an improved electron gun structure comprising a first electrode, a second electrode, a third electrode, a fourth electrode, an anode electrode and a convergence cup for focusing three electron beams radiated from cathodes arranged in line. Said electron gun further comprises second quadrupole lens-forming electrodes consisting of a second static electrode having a static voltage applied thereto and a second dynamic electrode disposed opposite to the second static electrode and having a dynamic voltage applied thereto; third quadrupole lens forming electrodes consisting of a third static electrode having a static voltage applied thereto, and a third dynamic electrode which is disposed opposite to the third static electrode and a dynamic voltage is applied thereto; and fourth quadrupole lens forming electrodes consisting of a fourth static electrode to which a static voltage is applied, and a fourth dynamic electrode which is disposed opposite to the fourth static electrode and a dynamic voltage applied thereto.